Question

The standard reduction potentials at 298 K for the following half-cell reactions are given:
$Z{n^{2 + }}(aq) + 2{e^ - } \rightleftarrows Zn(s);\,\,\,\,\, - 0.762\,V$
$C{r^{3 + }}(aq) + 3{e^ - } \rightleftarrows Cr(s);\,\,\,\,\,\, - 0.74\,V$
$2{H^ + }(aq) + 2{e^ - } \rightleftarrows {H_2}(g);\,\,\,\,\, + 0.00\,V$
$F{e^{3 + }}(aq) + {e^ - } \rightleftarrows F{e^{2 + }}(aq);\,\,\,\, + 0.77\,V$
Which one of the following is the strongest reducing agent
(A) $Zn(s)$
(B) $Cr(s)$
(C) ${H_2}(s)$
(D) $F{e^{2 + }}(aq)$

Answer 1

In order to the question, first we should know the relation between Standard reduction potentials and the reducing agent then after we have to discuss which is the strongest reducing agent among the given compounds. And we will also discuss what is the standard reduction potential.

Complete answer: Zinc is the strongest reducing agent in the following above given reactions because the standard reduction potentials of the Zinc, which is given, is the most negative than others. According to Oxidation and Reduction; the reducing agent is stronger when it has a more negative reduction potential and weaker when it has a more positive reduction potential.
Zinc is the strong reducing agent among $Cr(s)$ , ${H_2}(s)$ and $F{e^{2 + }}(aq)$ because zinc is higher in the activity series in comparison to all the given compounds. Zinc is oxidised more easily than the given other compounds. The electrode where oxidation takes place is called anode. In this case, zinc anode slowly depreciates due to loss of zinc metal while the cell operates.
Now, we should also know about the standard reduction potential: Galvanic cells have positive cell potentials, and all the reduction reactions are reversible. The reaction at the anode will be the half-reaction with the smaller or more negative standard reduction potential.

Hence the correct option is (A).

Note: The zinc causes the sulfur to gain electrons and become reduced and so the zinc is called the reducing agent. The oxidizing specialist is a substance that causes oxidation by tolerating electrons. The lessening specialist is a substance that causes decrease by losing electrons.